The present invention relates generally to force measuring devices, and more specifically to an improved device for measuring and providing an accurate readout of the tracking force of the stylus of a phonograph cartridge.
A phonograph cartridge contains a stylus which generally tracks the grooves of a record with a force of approximately 0.5 to 4 grams measured at the stylus tip. It is important that the stylus tracking force be determined and accurately established, since either too high or too low a stylus tracking force may cause damage to the record grooves and result in an audible degradation of the sound produced in the reproduction process. When such damage occurs to the record, it is irreversible.
Over the years a number of different devices have been proposed and used to measure the tracking force of a phonograph stylus. These devices have generally utilized a beam balance arrangement in which the phonograph stylus is placed at one end of a pivotable bar and a sliding weight is moved on a calibrated scale at the other end until the bar is balanced. These devices have suffered from a relative difficulty of use, including a difficulty in reading the often small indication of the measured force. Certain of these devices suffer from inaccuracy and a lack of repeatable measurements of the stylus force. Furthermore, the operation of certain of the prior devices may cause the user to damage the stylus by its being dropped during the measurement operation.
The present invention provides an improved stylus force gauge that is simple to use, and which provides an indication that can be clearly read and understood by the user. The stylus is placed on the tip of a measuring flexure extending from the body of the device and an illuminated discrete, digital or numeric display can be thereupon directly read to indicate the tracking force of the stylus. Thereafter the user may adjust the tone arm to achieve the optimum desired tracking force. The stylus force gauge of the invention provides for first and second scales of measurements to cover two, possibly overlapping force ranges. No balancing, calibration or other adjustments need be made by the user to employ or read the device.
It is accordingly an object of this invention to provide an improved force measurement device in which an analog, numeric or digital display of the measured force is provided.
It is another object of this invention to provide a force measurement device which is particularly suitable for use as a phonograph stylus tracking force gauge.
It is another object of this invention to provide a force gauge that does not require user adjustment.
It is another object of this invention to provide a force gauge of the type described having two separate measurement scales and which is easily switched between the two scales.
It is another object of this invention to provide a force gauge that minimizes the possibility that the user will damage the item whose force is to be measured.
It is a further object of the invention to provide a force measuring gauge in which a relatively small deflection of a force-sensing member is directly converted to easily readable form.
To these ends the present invention provides a device for measuring small forces such as tracking force of a phonograph cartridge or stylus. The device includes an elastic flexure member having an electric contact for engagement with an encoder. As the flexure member is deflected by an amount proportional to the force being measured, various contacts on the encoder are activated to provide discrete electrical signals. The signals are then used to drive a discrete visual display of the measured force. The display may be analog, numeric or digital and the reading of the display is directly related to the deflection of the flexure member. The device may also include a mechanism for providing a second point of deflection for the flexure member and a second visual scale to provide either greater precision or a greater range of measurement.